In general, a railroad vehicle (hereinafter referred to as “vehicle”) has a main motor (hereinafter referred to as “motor”) mounted on a bogie arranged below a body of the railroad vehicle. The rotating force of this motor is transmitted to wheels via gear mechanisms and joints, which causes the vehicle to run.
There is a growing need for a motor having an extended maintenance cycle, i.e., a motor requiring less maintenance. Accordingly, a totally-enclosed motor has been developed to satisfy this need.
This motor includes a stator core having a stator coil arranged on an inner peripheral side of a cylindrical frame and a housing and a bracket attached to both end sides of the frame to constitute an enclosed case, wherein each of the housing and the bracket includes bearings. A rotor shaft extends in the enclosed case. Both end portions of the rotor shaft are rotatably supported by the bearings. A rotor core is attached to a central portion of the rotor shaft, and the rotor core is located inside of the stator core. In the enclosed case, partition plates are attached to both end portions of the rotor shaft, and a labyrinth seal portion is formed between the bracket and an outer peripheral portion of each partition plate.
Recently, a permanent magnet motor is used more often in order to reduce heat of a rotor and to achieve a compact motor. In the permanent magnet motor, a permanent magnet, instead of a squirrel cage rotor, is inserted into a rotor core.
In the motor having the above structure, outside air does not circulate in the motor. Therefore, the inside of the motor is not contaminated with dust, and it is possible to save labor by eliminating the necessity of disassembling the motor to clean the inside. However, the bearings are lubricated with grease filled in bearing portions. The oil lubrication grease deteriorates as the motor operates, and it is necessary to replace the oil lubrication grease. The replacement of the oil lubrication grease is carried out upon disassembling the motor, which takes a lot of labor and time.